RELATIONSHIP BETWEEN HEART RATE VARIABILITY AND HYPOTENSION WITH BRADYCARDIA FOLLOWING SPINAL ANAESTHESIA IN PATIENT UNDERGOING ELECTIVE SURGERY

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T.F. Okanlawon¹, O.R. Eyelade¹, A.A. Adebiyi²

1. Department of Anaesthesia, College of Medicine, University of Ibadan/University College Hospital, Ibadan,
2. Department of Medicine, College of Medicine, University of Ibadan/ University College Hospital, Ibadan, Nigeria

Abstract

Background: Hypotension is a common complication of spinal anaesthesia and occurs due to the sympatholytic effect of local anaesthesia on the cardiovascular system and consequence effects on the autonomic nervous system. Heart rate variability (HRV) is currently a well-known predictive tool for hypotension and the commonly associated bradycardia.

Objective: To evaluate the relationship between preoperative measured HRV and hypotension with bradycardia among patients undergoing elective surgeries under spinal anaesthesia.

Method: Eighty-four patients aged between 18 and 65 years were recruited. HRV measurements were taken immediately after electrocardiographic (ECG) tracing according to the North American Society for Pacing and Electrophysiology (NASPE). Pre and intraoperative heart rate (HR), systolic and diastolic blood pressure and mean arterial blood pressure were monitored and recorded every 5 minutes from induction of spinal anaesthesia till the end of surgery. Multivariate analysis was used to determine the association between development of hypotension, bradycardia and age, systolic and diastolic blood pressure and Heart Rate Variability in the low frequency (LF) and high Frequency (HF) domains.

Results: Hypotension occurred in 55 patients (65.5%). Age (p= 0.015), base line systolic blood pressure (p=0.003) and base line diastolic pressure (p=0.027) were significantly associated with the development of hypotension. Low frequency (LF) was significantly associated with the development of hypotension, while high frequency (HF) was significantly associated with bradycardia.

Conclusion: Heart rate variability was useful in predicting development of hypotension and bradycardia in patient undergoing elective surgery under spinal anaesthesia.

Keywords : Spinal anaesthesia, Heart rate variability, Spinal hypotension, Bradycardia

Introduction

Hypotension is a common and severe complication of spinal anaesthesia. It is a physiological response of the cardiovascular system to the sympatholytic effect of the local anaesthetic agent used and it occurs in a third of all patients undergoing spinal anaesthesia.¹

Decrease in systemic vascular resistance precedes the onset of hypotension that usually develops rapidly within the first 5-20 minutes of induction of spinal anaesthesia and this period is considered the most critical period for the patient.²

The definition of spinal hypotension varies according to the criteria used. Using the Mean Arterial Blood Pressure (MAP), it has been defined as a decrease in MAP more than 30% from the baseline.^3,4 Based on the systolic blood pressure, it has been defined as systolic blood pressure < 90 mmHg while bradycardia was defined as a heart rate less than 60 beats per minute.² Bradycardia usually occurs within 5 -20 minutes of spinal anaesthesia, though it may occur much later in some patients

The risk factors that have been identified to be associated with higher incidence of hypotension and bradycardia includes age, weight, BMI, amount of colloid infusion given before puncture, chronic alcohol consumption, American Society of Anesthesiologist (ASA) physical status, preoperative history of hypertension, long term antihypertensive therapy, and frequency of puncture.^2,3,5

In an attempt to reduce the occurrence and severity of hypotension and bradycardia in patients undergoing spinal anaesthesia, recent research efforts have been to predict the occurrence of spinal induced hypotension and bradycardia preoperatively.⁵The ability to predict the occurrence and severity of spinal induced hypotension will enable adequate preoperative preparation and will potentially help in reducing the incidence of hypotension. It would also lead to improved outcome for patients managed for hypotension.^{5, 6}

The difference between a person’s lowest and highest heart rate is a reflection of the heart rate variability.^7-9 Unlike the heart rate that can be calculated by counting the pulse, electrocardiography is the gold standard for measuring Heart Rate Variability (HRV).^8,10

Heart rate variability (HRV) is a very good measure of the efficiency and performance of the cardiovascular system.^9,11,12 Low HRV is indicative of reduced parasympathetic cardiac control and has been associated with disorders ranging from diabetes mellitus to sleep problems, as well as difficulty regulating emotions. Determination of the HRV preoperatively may therefore be a useful tool in predicting the occurrence of hemodynamic events, especially in high risk patients who are at risk of severe perioperative complications. This study was carried out to preoperatively determine the relationship between the incidence of post spinal hypotension and bradycardia in patients using preoperative assessment of heart rate variability parameters